How do I create a UIColor from RGBA?

问题

I want to use NSAttributedString in my project, but when I'm trying to set color, which isn't from the standard set (redColor, blackColor, greenColor etc.) UILabel displays these letters in white color. Here is my line of this code.

[attributedString addAttribute:NSForegroundColorAttributeName
                         value:[UIColor colorWithRed:66
                                               green:79
                                                blue:91
                                               alpha:1]
                         range:NSMakeRange(0, attributedString.length)];

I tried to make color with CIColor from Core Image framework, but it showed the same results. What should I change in my code to perform it in right way?

Thx for answers, guys!

回答1:

Your values are incorrect, you need to divide each color value by 255.0.

[UIColor colorWithRed:66.0f/255.0f
                green:79.0f/255.0f
                 blue:91.0f/255.0f
                alpha:1.0f];

The docs state:

+ (UIColor *)colorWithRed:(CGFloat)red
                    green:(CGFloat)green
                     blue:(CGFloat)blue
                    alpha:(CGFloat)alpha

Parameters

red The red component of the color object, specified as a value from 0.0 to 1.0.

green The green component of the color object, specified as a value from 0.0 to 1.0.

blue The blue component of the color object, specified as a value from 0.0 to 1.0.

alpha The opacity value of the color object, specified as a value from 0.0 to 1.0.

Reference here.

回答2:

One of my favourite macros, no project without:

#define RGB(r, g, b) [UIColor colorWithRed:(float)r / 255.0 green:(float)g / 255.0 blue:(float)b / 255.0 alpha:1.0]
#define RGBA(r, g, b, a) [UIColor colorWithRed:(float)r / 255.0 green:(float)g / 255.0 blue:(float)b / 255.0 alpha:a]

Using like:

[attributedString addAttribute:NSForegroundColorAttributeName
                         value:RGB(66, 79, 91)
                         range:NSMakeRange(0, attributedString.length)];

回答3:

UIColor uses a range from 0 to 1.0, not integers to 255.. Try this:

// create color
UIColor *color = [UIColor colorWithRed:66/255.0
                                 green:79/255.0
                                  blue:91/255.0
                                 alpha:1];

// use in attributed string
[attributedString addAttribute:NSForegroundColorAttributeName
                         value:color
                         range:NSMakeRange(0, attributedString.length)];

回答4:

Please try the code

[attributedString addAttribute:NSForegroundColorAttributeName value:[UIColor colorWithRed:77.0/255.0f green:104.0/255.0f blue:159.0/255.0f alpha:1.0] range:NSMakeRange(0, attributedString.length)];

Label.textColor=[UIColor colorWithRed:77.0/255.0f green:104.0/255.0f blue:159.0/255.0f alpha:1.0];

UIColor's RGB components are scaled between 0 and 1, not up to 255.

回答5:

Since @Jaswanth Kumar asked, here's the Swift version from LSwift:

extension UIColor {
    convenience init(rgb:UInt, alpha:CGFloat = 1.0) {
        self.init(
            red: CGFloat((rgb & 0xFF0000) >> 16) / 255.0,
            green: CGFloat((rgb & 0x00FF00) >> 8) / 255.0,
            blue: CGFloat(rgb & 0x0000FF) / 255.0,
            alpha: CGFloat(alpha)
        )
    }
}

Usage: let color = UIColor(rgb: 0x112233)

来源：https://stackoverflow.com/questions/13224206/how-do-i-create-a-uicolor-from-rgba

标签

ios

objective-c

rgb

nsattributedstring

uicolor